SIMD processors (SIMD: Single Instruction Multiple Data) are able to process a number of data streams in parallel, with only one program being used. They are thus used, for example, in telephone systems, where the speech data from a number of channels must be processed, and must be output on a transmission line, simultaneously.
Conventional SIMD processors have two or more arithmetic units, which are also referred to as ALUs (ALU: Arithmetic Logic Unit), and a program which is stored in a memory and is carried out simultaneously by all the arithmetic units. This program generally contains a series of subroutines, which are called by the main program, for example by means of a “Call command”.
The subroutines are normally also processed simultaneously by the arithmetic units. However, it is possible for a specific section of the main program or a subroutine to be carried out only by specific ones of the arithmetic units, but not by others. For example, a conditional call command may occur, whose jump condition is satisfied only by specific arithmetic units which are intended to process that subroutine.
In this case, conventional SIMD processors would produce incorrect results, since the program is always carried out simultaneously by all the arithmetic units in these processors.
The object of the present invention is thus to provide a method for controlling an SIMD processor as well as such an SIMD processor, in which predetermined program sections, in particular subroutines, can be carried out by only some of the arithmetic units.
This object is achieved by the features specified in patent claim 1 and in patent claim 7. Specific embodiments of the invention are the subject matter of dependent claims.
The fundamental idea of the invention is to control an SIMD signal processor such that those arithmetic units are switched off or deactivated which are not intended to carry out a specific program section, in particular a subroutine. These arithmetic units are then switched on or activated again at the end of that program section. According to the invention, the arithmetic units are controlled by means of flags (markers) which are specific to specific arithmetic units. Each arithmetic unit is preferably allocated its own flag, which indicates whether that arithmetic unit should or should not be deactivated.
Said flags are generally variables which are set or reset and, in particular, can be linked to predetermined conditions. The default setting for the flags is, for example, “active” (set), that is to say the arithmetic units are intended to remain switched on.
In order to find out which of the arithmetic units are intended to remain switched on and which are intended to be switched off, the flags of the arithmetic units are first of all read and evaluated. Those arithmetic units whose associated flag was not set are then switched off.
Finally, the program section or the subroutine is carried out only by those arithmetic units whose flag was set.
The reading and evaluation of the flags which are specific to arithmetic units are preferably carried out before the program is intended to jump into a subroutine (that is to say in the case of a call command, in particular in the case of a conditional call command).
The subroutine is preferably not called when all the flags are inactive.